Sights of the above general type are often called red-dot sights and are well known in the art. Representative examples of such sights are shown in U.S. Pat. Nos. 4,346,995 and 5,189,555.
For the intended result, namely that the user of the sight mounted on the barrel of a gun can see the target with its surroundings together with an aiming point; i.e., a red dot, in the sight, so that the target can be hit when the red dot is placed thereon, the basic requisite is that the concave side of the optical element be parabolically shaped. Another important feature is that an opposite convex side causes as little deviations of the incoming light beams as possible over its entire surface, so that distortions of the image of the target and its surroundings in the sight are obviated.
Hitherto it has been customary to compose the optical element of two (or even more) sub-elements (with the partially reflective layer between them) in order to obtain a satisfactory, although not perfect result. These different sub-elements have been selected to provide different light refractive indices in order to correct for colour aberration and obtain a satisfactory sharp image. Nevertheless, the result has not been really impressive, especially towards the periphery of the elements. Normally, the optical elements have been made of glass.
With the development of material technology it has rather recently been suggested to manufacture the optical element in one piece from a plastic material. The suggested manufacturing method for such a plastic element is moulding.
The object of the present invention is to improve the optical characteristics of the sight.